The invention relates to a gas-discharge lamp including a fault protection circuit, and particularly to a gas-discharge lamp including a combination overvoltage-protection-and-ground-fault-interrupt circuit.
Safety agencies such as UL, CSA, and CE require output ground fault protection on electronic power supplies for neon signs and other gas discharge lamp applications. A ground-fault-interrupt circuit interrupts or deactivates the power supply in the event of a ground fault occurrence. In addition, these agencies set limits on the maximum output voltage that may be produced by the power supply. An overvoltage-protection circuit interrupts or deactivates the power supply in the event of an overvoltage condition. In order to prevent nuisance tripping and to ensure the fault trip occurs when the limiting value of ground fault current or output voltage is reached, it is desirable to make these circuits as accurate as possible. However, due to the competitive nature of the gas-discharge lamp market, these circuits should be as inexpensive as possible. Thus, it would be beneficial to have a sensitive and inexpensive circuit for detecting both a ground-fault condition and an overvoltage condition.
Accordingly, in one embodiment, the invention provides a gas discharge lamp including a power supply connectable to a load (e.g., one or more gas-discharge tubes), and an overvoltage-protection-and-ground-fault-interrupt (OVP/GFI) circuit interconnected with the power supply. The OVP/GFI circuit includes an overvoltage-protection (OVP) sub-circuit that deactivates the power supply when an overvoltage condition is detected, and a ground-fault-interrupt (GFI) sub-circuit that deactivates the power supply when a ground-fault condition is detected.
In a second embodiment, the invention provides a gas-discharge lamp including a power supply having a secondary winding connectable to a load, and an overvoltage-protection-and-ground-fault-interrupt (OVP/GFI) circuit interconnected with the power supply. The OVP/GFI circuit includes an overvoltage-condition-and-ground-fault-condition (OC/GFC) sensor that is operable to sense both an overvoltage condition being created by the power supply and a ground-fault condition being created in the secondary winding. The OC/GFC sensor is further operable to generate a fault signal when either condition occurs. The OVP/GFI circuit further includes a shut-down device interconnected with the OC/GFC sensor. The shut-down device deactivates the power supply from supplying power to the load upon receiving the fault signal.
Using one sensor or one circuit to sense a ground-fault condition or an overvoltage condition in a gas-discharge power supply helps to eliminate redundant components of separate ground-fault-interrupt and overvoltage protection sensors or circuits. This results in a reduction of overall cost in the sensor or circuit. Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following detailed description, claims, and drawings.